The following disclosure relates to a sheet conveying device and an image forming apparatus capable of detecting the height of sheets on a pressing plate.
There is conventionally known a sheet conveying device including: a pressing plate movable upward and downward while supporting a sheet; and a motor configured to move the pressing plate upward to a suppliable position at which the sheet is in contact with a supply roller and a separating roller. This sheet conveying device calculates the number of sheets supported on the pressing plate, i.e., a sheet remaining amount, based on a driving time and/or a rotation amount of the motor which is required for the pressing plate to move from the lowest position to the suppliable position.
In this sheet conveying device, a driving mechanism including a plurality of gears transmits a driving force from the motor to the pressing plate. However, there are backlash in the gears and looseness between a shaft and a bearing of the gear in the driving mechanism, for example. Thus, variations are caused in a length of time and a rotation amount of the motor from the start of driving of the motor to the start of actual upward movement of the pressing plate. These variations in the length of time and the rotation amount may cause an error in calculation of the number of sheets supported on the pressing plate.
To solve this problem, it has been developed a technique of using a sensor to detect a start of operation of a raising plate for moving the pressing plate upward, then determining the driving time and/or the rotation amount of the motor from the detection of the start of operation of the raising plate to a point in time when the pressing plate moved upward from the lowest position reaches the suppliable position, and then calculating the number of sheets based on this determined value.
Since the number of sheets is calculated as described above based on the driving time and/or the rotation amount of the motor from the start of operation of the raising plate for moving the pressing plate upward, it is possible to remove the variations in the driving time and the rotation amount of the motor which are caused in a period from the start of driving of the motor to the start of operation of the raising plate. This removal reduces an error in the calculated number of the sheets.